Temperature control device



July 28, 1959 M. D. MOFARLANE ETAL 2,897,333

' TEMPERATURE conmor. DEVICE Original Filed Nov. 9, 1955 3 Sheets-Sheetl Ja -var.

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July 28, 1959 M. D. M FARLANE ET AL 2,897,333

I TEMPERATURE CONTROL DEVICE Original Filed Nov. 9, 1955 3 Sheets-Sheet2 74 AMPLIFIER] WHI -w SUPPLY INVENTORS! jmlynardfl Mq'briane BandY(ecilA. G afts THEYR .AT'TQRAZE'K July 28, 1959 M. 0. M FARLANE ETAL2,397,333

TEMPERATURE CONTROL DEVICE Original Filed Nov. 9. 1955 3 Sheets-Sheet 37 "W -7 In 110 AMPuFlER I N VEN TORS' M 12/11 Warlane a (0017A (rafts.

THEYRAT'I VIDA/EX United States Patent Q TEMPERATURE CONTROL DEVICEMaynard D. McFarlane, Corona del Mar, and Cecil A.

Crafts, Pasadena, Calif, assignors to Robertshaw-Fulton ControlsCompany, Greenshurg, Pa., a corporation of Delaware Original applicationNovember 9, 1955, Serial No. 545,860. Divided and this application March27, 1957, Serial No. 648,974

7 Claims. (Cl. 219-20) This invention relates to heating control devicesand more particularly to devices wherein the heating medium consists ofa slurry of fusible material having a melting temperature of a value tobe controlled.

In systems requiring accurate temperature control for long periods oftime wherein temperature dilferentials do not exceed a few hundredths ofa degree and the system experiences varying ambient temperatureconditions or heat applications, accurate control has been extremelydifiicult if not impossible since present day thermostats are incapableof performing within such close tolerances. Such a system may comprise acrystal oscillator circuit wherein extreme frequency stability isrequired. Since crystal control units are susceptible to even a slighttemperature variation, drifting from the desired set frequency can beovercome only by immersing the crystal unit in an atmosphere having acontinuous constant temperature condition.

In the present invention which is a division of our application SerialNo. 545,860, filed November 9, 1955,

advantage has been taken of the physical property exhibited by materialsand alloys at their melting temperatures. The melting point of an alloyis an exactly reproducible and stable value, and may be prescribed andvaried by modifying the quantity of components which go to make up thealloy. At the melting temperature, advantage is taken of the latent heatof fusion of the material used so that this exact temperature ismaintained over a wide range of external temperature conditions.

At the melting temperatures, the materials consist of a slurry composedpartly of solid material and partly of liquid. Since the melting pointtemperature is independent of the ratio of liquid to solid, the slurrycan be maintained at constant internal temperature over a wide range ofheat application from a heating element or the like. In the use of anelectrical heating element, extremely accurate control of thetemperature of the crystal oscillator circuit can be maintained withintermittent or widely varying applications of power to the heatingelement. Since a change of state is involved at the desired temperature,which is the melting point of the alloy, the change in electricalresistance upon this change of state has been utilized to control theamount of power delivered to the heating element.

For example, with some compositions, there exists a change in resistanceof approximately 90% between the solid and liquid state of the alloy. Itis, therefore, apparent that the present invention utilizes acharacteristic of a fusible alloy which controls the application of heatto the system through a change occurring in the material itself. Thus,the melting temperature of the alloy at the point of change of state orat the so-called triple point not only regulates the heat applied to aheating space but it also acts inherently as a thermostat to control theapplication of heat to the entire system.

In another embodiment of the present invention, the proportional changein viscosity of the alloy in transform ing from the solid state to theliquid state, is utilized to 2,897,333v Q6 Patented July 28, 1959 eifectheating conditions of the alloy. Since the slurry consists of a mixtureof liquid and solid material, it will be apparent, that the viscosity ofthe slurry is a function of the change of state, and in fact, theviscosity will vary over a large large range as the material changesfrom completely solid to completely liquid. A novel arrangement of amixing arm and circuit means for rotating the same is utilized to effectaccurate temperature control of the slurry.

Therefore, it is the principal object of the present invention toutilize the melting temperature at which the change of state of amaterial occurs to regulate both the heat output of the material and theheat producing medium applied to the material.

Another object of the present invention is to accurately control thetemperature of a space within very precise limits for indefinite periodsof time under varying conditions of heat application.

Other objects and advantages will appear from the fol lowingspecification taken in conjunction with the accompanying drawingswherein:

Fig. l is a schematic View of a typical arrangement of the presentinvention;

Fig. 2 is a similar schematic View of another circuit arrangement;

Fig. 3 is a circuit diagram of another modification of the arrangementshown in Fig. 2;

Fig. 4 is a circuit diagram of still another modification of the presentinvention; and

Fig. 5 is a schematic view showing still another arrangement of thepresent invention.

Referring more particularly to Fig. 1, there is shown an inner container10 which serves as an oven or heating space wherein a crystal oscillatorunit may be housed. An outer container 12 completely encases thecontainer 19 and is suitably lined with insulation 14 for reducing heatlosses and hence the power supplied as will presently appear. Completelyfilling the outer container 12 is a fusible conductive alloy '16composed of materials which will fuse when heated to a prescribedmelting temperature, and which is so chosen as to possess a high latentheat of fusion.

As an example:

For a temperature of C., this alloy is satisfactory: Percent Sodium 60Thalium 40 For C., the following has been found satisfactory:

For 118 C., the following has been found satisfactory:

Tin 47 Indium 53 For 120 C., the following has been found satisfactory:Thalium 73 Gold 27 or Indium 75 Cadmium 25 Potassium alone may be usedat a temperature of 63.7 C.; sodium alone for 97.8 C. and caesium alonefor 285 C.

A pair of electrodes 18, 20 are immersed in the ma terial 16 and areconnected to the terminals of a low voltage-high amperage battery 22 byconductors 24, 26 through a regulating resistor 28. In order toelectrically insulate the conductive material 16 from the rest of theapparatus, the containers 10 and 12 are preferably made of insulative ornon-conductive material. It will be obvious that any other suitablemeans may be employed to insulate the material 16, such as by coatingthe containers 10 and 12 with non-conductive material. It will also beapparent that the containers 10 and 12 may be made from conductingmaterial and used as electrodes instead of the electrodes 18, 20. Inaddition, an agitator (not shown) may be employed for mixing thematerial when in a slurry state to maintain even distribution of thesolid-liquid characteristics of the ma terial 16.

In operation, since the material 16 is of a conducting nature, a currentwill flow from the battery 22 through the material 16, and the passageof this current will cause the liquefaction of the material 16. As heatis absorbed in the slurry state of the material 16 due to this currentflow, the resistance increases, and therefore, the current is decreased.This process will reach an equilibrium when the heat generated in thematerial 16 exactl-yequals the heat lost by conduction, radiation, etc.from the container 12. The rheostat 28 serves as a means for adjustingthe current fiow so that this equilibrium point may be established atthe temperature of liquefaction of the material 16.

Accurate temperature regulation is obtained since the material 16 ischosen to have a high latent heat of fusion so that when the material 16is in a slurry state, any heat loss through radiation, conduction, etc.,causes solidification and involves only the heat of fusion withoutaffecting the temperature of the material 16. On the other hand, anygain in heat, say by an overload from the battery '22 or from any otherextraneous source, will result only in absorption of this heat as theslurry mass becomes more liquid than solid. In addition, due to theinherent balancing effect of the resistance-current values, the systemis completely self-regulating once the desired characteristics have beenestablished by adjustment of the rheostat 28.

In the modification shown in Fig. 2, the material 16 is heated by aresistance winding in the form of a heater element 30 wound around theouter container 12 and a pair of electrodes 32, 34 immersed in thematerial 16 which serve to sense the resistance within the material 16.The heater element 30 is connected by a conductor 36 to one terminal ofa battery and to a switch arm 40 by a conductor 42. To complete theheating circuit to the heater element 30, the switch arm 40 is adaptedto engage and be normally biased from a stationary contact 44 connectedby a conductor 46 to the battery 38.

Actuation of the switch arm 40 into engagement with the stationarycontact 44 for effecting energization of the heater element 30 isprovided for and takes the form of a relay 48 having a pair of coils t),52, one side of each being connected by a wire 54. The sensing electrode34 is connected by a conductor 56 to the other side of the coil 50. Asecond conductor 58 connects the sensing electrode 32 with the otherside of the coil 52 through a rheostat 60 which serves to adjust theresistance within the sensing circuit at which the relay will beenergized when the material 16 has reached a predetermined liquid-solidratio in accordance with intrinsic resistance therein. A small battery62 of low voltage and amperage is connected in parallel with the coil 52and the rheostat 60 and cooperates with the rheostat 6!) for permittingfiner adjustment and energization of the relay 48. V

In operation, the current flow in the heater element 30 is turned on andoh by the relay 48 in accordance with the internal resistance of thematerial 16 when in a predetermined stage of the slurry condition. Asthe liquid content in the slurry decreases, the resistance drops .4 thuspermitting an increase in the current flow therethrough whereby therelay 48 becomes energized to attract the switch arm 40 into engagementwith the contact 44. Upon this occurrence, additional power is suppliedto the heater element 30 from the battery 38 and more heat is absorbedby the material 16 to effect a greater solid to liquid ratio. When theliquid content and subsequently the resistance of the material rises,the relay 48 is deenergized and the switch arm 40 will open to cut offpower to the heater element 30.

The modification shown in Fig. 3 is similar to that disclosed in Fig. 2except that the relay :8 and its associated circuitry is replaced by apower amplifier. The sensing electrodes 32, 34 in the material 16 areconnected by conductors 64, 66 respectively to one arm of a resistancebridge generally indicated by the reference numeral 68, the diagonal ofwhich is connected by a pair of wires 70, 72 to the input stage of anamplifier 74. A pair of conductors 76, 78 connect the heater element 30to the output stage of the amplifier 74 which derives its power from apower supply 80 through a pair of conductors 82. To complete the bridgecircuit, power is supplied to the bridge 68 from the power supply 80through a pair of wires 84, 86 in the usual manner.

The amplifier 74 may be of any conventional type wherein the input stageis adapted to sense the unbalanced voltage from the bridge 68, amplifythe voltage in proportion to the electrical resistance of the material16 as reflected by the bridge 68 and energize the heater element 30 to adegree of heat proportional to the resistance of the material 16. Arheostat 88 is connected to the wire 84 and serves to adjust the powersupply to the bridge 68 thereby varying the operating level at which theamplifier 74 is required to respond.

The advantage of this embodiment over the arrangement shown in Figs. 1and 2. is that there will be no on-01f condition in the heater element30 since the heater element will be supplied with current from theamplifier 74 at all times; however, this current will be varied inaccordance with the resistance change determined by the sensing elementsat the input of the amplifier 74. Under normal operating conditions, theamplifier 74 will reach a stable operating condition, and there will bevery little current change experienced in the heater element 30.

The embodiment of Fig. 4 is similar to that of Fig. 3 and includes asaturable reactor in the output stage of the amplifier section of thesystem. As in the previous modifications, for simplicity, likecomponents will be designated by like numerals.

Instead of directly energizing the heater element 30, the amplifiedsignal from the amplifier 74 is fed to a saturable reactor 90 by a wire92 to control the current to the heater element 30. As shown in Fig. 4,the conductors 76, 78 from the heater element 30 are connected to theoutput stage of the reactor 90 and the power supply 80 is connected tothe reactor by wires 94. In this arrangement, the amplifier 74 may be ofthe low gain type for controlling the input winding (not shown) of thereactor 90.

While the embodiments of Figs. 1, 2, 3 and 4 are directed to the changeof resistance characteristics in the slurry state of the fusiblematerial 16, another characteristic is peculiar to the change of stateof the material 16. Since the slurry consists of a mixture, in variousproportions, of the liquid and solid material, it will be apparent thatthe viscosity of the slurry is a function of the change of state, and infact, it has been found that the viscosity will vary over a very largerange as the material changes from entirely solid to entirely liquid. Inthe embodiment of Fig. 6, a measure of viscosity is used as a sensingelement for the heating control of the material 16.

In Fig. 5, a pair of mixing arms are immersed in the material 16 betweenthe containers 10 and 12 and is connected to the operating shaft 102 ofan electric motor 104 for rotation therewith. A pair of wires 106, 108having a resistor 110 in series therewith connects the motor 104 to asource of electric current L1, L2 in the usual manner for energizing themotor 104.

The heater element 30 which is Wound conductively around the outercontainer 12 is adapted to be energized by an amplifier 112 through apair of conductors 114, 116 connected therebetween. The input stage ofthe amplifier 112 is connected across the resistor 110 by a pair ofwires 118, 120, and a wire 122 connected between the source L1 and theamplifier 112 serves to complete the power supply to the amplifier 112from the source L1, L2 through the wires 120, 122.

In operation, the voltage drop across the resistor 110 is proportionalto the current drawn by the motor 104, which is in turn proportional tothe mechanical resistance offered by the slurry of the material 16 tothe rotation of the steering arms 100. Thus the greater the percentageof solid material 16 in the slurry, the higher the mechanicalresistance, the greater the current drawn by the motor 112, the greaterthe voltage drop across the series resistor 110 and consequently, thegreater the signal ap plied to the amplifier. Since the output of theamplifier 112 is connected to the heater element 30, as the mechanicalresistance is increased due to an increase in the solid content of theslurry content, the power to the heater element 30 will be increased bythe amplifier 112.

It will be apparent from the foregoing that the illustrated embodimentsprovide new and improved control devices for maintaining steady heat toa space within precise temperature limits and which utilizes variouscharacteristics of a slurry of fusible material to control theapplication of heat to the slurry so that the material is nevercompletely solid or completely liquid. It will also be obvious to thoseskilled in the art that the illustrated embodiments may be variouslychanged and modified, or features thereof, singly or collectivelywithout departing from the scope of the invention or sacrificing all ofthe advantages thereof, and accordingly the disclosure herein isillustrative only and the invention is not limited thereto.

It is claimed and desired to secure by Letters Patent:

1. In a condition controlling device, the combination comprising acontainer, a heating element of conductive fusible material disposed insaid container and having a predetermined fusion temperature and a highlatent heat of fusion, a second container carried within said firstmentioned container in heat transfer relationship with said heatingelement, means associated with said first mentioned container forheating said heating element to the fusion temperature thereof, andcircuit means in cluding switch means and a pair of sensing electrodesconnected to said heating element for controlling the cnergization andde-energization of said heating means in response to changes in theresistance of said heating element.

2. A temperature stabilizing and control apparatus comprising a firstcontainer, a second container carried within said first container, aheating element of electrically conductive fusible material having apredetermined fusion temperature and a high latent heat of fusioncarried within said first container in heat transfer relationship withsaid second container, means associated with said first container forheating said heating element to the fusion temperature thereof, asensing circuit including a pair of electrodes connected to said heatingelement for sensing the change in electrical resistance of said heatingelement at the fusion temperature thereof, and circuit means including aswitch operatively associated with said heating means for controllingthe energization and de-energization of said heating means in responseto changes in the resistance of said heating element sensed by saidsensing circuit.

3. In a temperature control device, the combination comprising acontainer, a heating element of electrically conductive fusible materialin said container having a predetermined fusion temperature and a highlatent heat of fusion, a second container carried within said firstmentioned container in heat transfer relationship with said heatingelement, means including an electrical circuit associated with saidfirst mentioned container for heating said heating element to the fusiontemperature to produce a liquid-solid state thereof, switch means insaid electrical circuit and being movable between open and closedpositions for controlling the energization and de-energization of saidheating means, circuit means including a pair of electrodes connected tosaid heating element for sensing the change in resistance thereof inresponse to a change in the liquid-solid ratio thereof, electromagneticmeans in said circuit means energized and de-energized in response to apredetermined change in a resistance of said heating element and beingoperable to control the movement of said switch means between saidpositions, and means in said circuit means for selectively adjusting theresistance thereof to effect energization and de-energization of saidelectromagnetic means at a predetermined liquid-solid ratio of saidheating element.

4. In a temperature control device as claimed in claim 3 wherein saidcircuit means includes a source of potential connected in parallel withsaid electromagnetic means and said last named means.

5. In a condition controlling device, the combination comprising aheating means, a heating element including a confined mass of fusiblematerial having a heat of fusion temperature coincident with apredetermined temperature to be maintained thereby and positioned torespond to the temperature output of said heating means, and circuitmeans including plural electrodes disposed in the fusible material ofsaid heating element and operatively connected to said heating means forcontrolling the supply of heat from said heating means in accordancewith changes in the resistance of said heating element.

6. In a system for controlling a condition comprising, circuit meansadapted to be operatively connected to a heating means having an outputtemperature variable in accordance with condition changes in saidcircuit means, a heating element of fusible material variable incondition and positioned to respond to the output temperature of saidheating means, and plural electrodes disposed in the fusible material ofsaid heating element and operatively connected to said circuit means andvarying the condition thereof whereby the output temperature of theheating element is varied in response to condition variations in thefusible material of said heating element.

7. In a condition controlling device, the combination comprising acontainer, a heating element of fusible material in said containerhaving a predetermined fusion temperature and a high latent heat offusion, means carried within said container in heat transferrelationship with said heating element, means for heating said heatingelement to the fusion temperature thereof, circuit means includingswitch means for controlling the energization of said heating means, anda pair of electrodes disposed in the fusible material of said heatingelement and being operatively connected to said switch means andcontinuously actuating same in accordance with resistance variations ofsaid heating element.

References Cited in the file of this patent UNITED STATES PATENTS1,367,122 Chubb et al. Feb. 1, 1921 1,863,253 Polin June 14, 19321,921,432 Stallard Aug. 8, 1933 2,516,570 Hartwig et al. July 25, 19502,524,886 Colander et al. Oct. 10, 1950 2,640,089 Gilbert May 26, 19532,726,312 Dunlap, Jr. Dec. 6, 1955 2,767,296 Welch Oct. 16, 1956

